1. Field of the Invention
The present invention relates to spread spectrum communication systems using PN coding techniques and, more particularly, to acquiring a phase of the PN code.
2. Prior Art
Spread spectrum (SS) systems, which may be CDMA systems, are well known in the art. SS systems can employ a transmission technique in which a pseudo-noise (PN) PN-code is used as a modulating waveform to spread the signal energy over a bandwidth much greater than the signal information bandwidth. At the receiver the signal is de-spread using a synchronized replica of the PN-code.
There are, in general, two basic types of SS systems: direct sequence spread spectrum systems (DSSS) and frequency hop spread spectrum systems (FHSS).
The DSSS systems spread the signal over a bandwidth fRF±Rc, where fRF represents the center bandpass carrier frequency and Rc represents the PN-code maximum chip rate, which in turn is an integer multiple of the symbol rate Rs. Multiple access systems employ DSSS techniques when transmitting multiple channels over the same frequency bandwidth to multiple receivers, each receiver having its own designated PN-code. Although each receiver receives the entire frequency bandwidth only the signal with the receiver's matching PN-code will appear intelligible, the rest appears as noise that is easily filtered. These systems are well known in the art and need not be discussed further. As noted, the DSSS system PN-code sequence spreads the data signal over the available bandwidth such that the carrier appears to be noise-like and random to a receiver not using the same PN-code.
In communication systems having multiple central base stations or network access points (AP) and multiple subscriber units or consumer premise equipment (CPE), e.g., fixed or mobile units, the CPE may receive and decode signals transmitted by each of the APs. It will be appreciated that in burst communication systems it is desirable to provide a method and system to quickly determine the strongest or desirable transmitting station; and to quickly open-loop synchronize with a forward burst signal communicated by the transmitting station.